The overall objective of the studies proposed is to gain an understanding of how basic attentional processes of stimulus alerting (automatic attention), sustaining attention, and selective attention are related to the behavioral and cognitive symptoms of children with Attention Deficit Hyperactivity Disorder (ADHD). The applicant is one of six investigators selected to carry out a large scale study of the long term treatment effects of drug and psychosocial therapies and their combination (the multi-site treatment of ADHD or MTA study). The studies proposed in this application address questions not otherwise studied in the MTA program, by using the assessment data approved by the MTA Steering Committee, as well as a large database already available from the applicant's ADHD clinic. Using this database, measures of alerting, sustained attention, and selective attention are derived from a specially constructed continuous performance test (CPT) and a test of directed spatial attention. These measures are examined for developmental age and gender effects in a cross- sectional sample of 468 males and females ranging from 4 to 56 years of age. Principal hypotheses are that automatic attention and sustained attention will be related to symptoms of inattention seen behaviorally by parents and teachers, while measures of selective attention will relate primarily to symptoms of behavioral disinhibition, i.e. hyperactive- impulsive behavior as measured by parent and teacher ratings. Another study uses 300 children from the MTA study who will have deceived the same measures just described. That study will use attentional measures to predict dose-response effects on behavioral and academic functioning found in the double-blind counterbalanced titration trial of 3 doses of methylphenidate (MPH) and placebo. An additional measure of stimulus arousal is derived from simultaneous auditory and visual stimulation during the CPT. At the applicant's site, 50 children will also provide a measure of polysensory stimulation of arousal on the vertex evoked potential, used as a predictor of dose-response relationships. Similar measures are proposed for study in 50 adult ADHD and matched normals. Additionally, these subjects will receive stimulation with visual stimuli (reversing checkerboard) of different spatial frequency, to measure visual evoked potentials at left and right occipital locations. This study examines the possibility that magnocellular pathways involved in automatic attention are impaired in ADHD.